This paper presents an analytical development for the Nyquist trajectory of the closed loop system of a Voltage Source Inverter with resonant control strategy. Both inner current loop and outer voltage loop are taken into account, and the interaction between them is studied. The stability boundaries depending on different parameters are determined. Firstly, the system is modelled and analysed in continuous time. Secondly, the analysis is conducted in the discrete time domain. A numeric study supported with graphical representations is provided for complex analytic situations.